Post by dougsanders on Dec 31, 2014 17:31:59 GMT -8
On page 521, Raising System, I am troubled by the first 2 paragraphs. Clear, simple, effective tools are important in an emergency. Not sure we are doing that.
"Raising systems. The 3:1 (Z) pulley system (fig. 24-5a)is usually the most efficient of the simple raising systems. Chapter 17, Glacier Travel and Crevasse Rescue, describes setting up a 3:1 system.
"If more mechanical advantage is needed, a 5:1 pulley system can be constructed in one of two ways: by adding a carabiner and a triple runner or cordelette that is 15 to 25 feet (5 to 8 meters) long (fig. 24-5b); or by adding a second traveling prusik and carabiner instead of a second pulley (fig. 24-5c). Where there is a very heavy load or only a few haulers, a second 3:1 system can be added to the pulling end of the first 3:1 pulley system to create a 9:1 (Z-on-Z) raising system (fig. 24-5d)."
Thoughts:
Given that a 9:1 is really only a 6-7:1 (90% efficient pulleys) a 9:1 is the best starting point for raising a 2-person load with a small party. The chapter used 2 teams of 2 as a model small team to remain in compliance with the Climbing Code.
The simplest technique for converting a compound 9:1 (3:1 on a 3:1) to a 5:1 is not described. Attaching the 2nd 3:1 to the 1st 3:1 with a biner at the traveling pulley, instead of a prusik, accomplishes this.
The 3:1 is taught for crevasse rescue. By using this building block even a Basic climber can setup an effective 9:1 rescue raising system (adding a second 3:1 to an initial 3:1.)
"Raising systems. The 3:1 (Z) pulley system (fig. 24-5a)is usually the most efficient of the simple raising systems. Chapter 17, Glacier Travel and Crevasse Rescue, describes setting up a 3:1 system.
"If more mechanical advantage is needed, a 5:1 pulley system can be constructed in one of two ways: by adding a carabiner and a triple runner or cordelette that is 15 to 25 feet (5 to 8 meters) long (fig. 24-5b); or by adding a second traveling prusik and carabiner instead of a second pulley (fig. 24-5c). Where there is a very heavy load or only a few haulers, a second 3:1 system can be added to the pulling end of the first 3:1 pulley system to create a 9:1 (Z-on-Z) raising system (fig. 24-5d)."
Thoughts:
Given that a 9:1 is really only a 6-7:1 (90% efficient pulleys) a 9:1 is the best starting point for raising a 2-person load with a small party. The chapter used 2 teams of 2 as a model small team to remain in compliance with the Climbing Code.
The simplest technique for converting a compound 9:1 (3:1 on a 3:1) to a 5:1 is not described. Attaching the 2nd 3:1 to the 1st 3:1 with a biner at the traveling pulley, instead of a prusik, accomplishes this.
The 3:1 is taught for crevasse rescue. By using this building block even a Basic climber can setup an effective 9:1 rescue raising system (adding a second 3:1 to an initial 3:1.)